We examined vegetation composition and its relation to environmen­ tal variables in the Sidlum area along the mediterranean coastal land of Egypt. The study area lies between 25° 09'-25° 35'E and 31° 32'­ 31° 15' N (about 1700knr), and extendi-.!or about 49 km between Buqbuq and Sallum on the egyptian-libyan frontier. It ii' included in the semi-desert vegetation zone with an attenuated desert climate. An analysis of vegetation along environmental gradients that prevail in the study area using the relative importance values of 55 perennials in 53 stands, fOllowed by multivariate data analysis was presented. Altogether, 1// i!JI'cie.' (75 perennials aw!3(, (';/ill,.:l,-) be!riJIo!I/CJ to 92 genera and 34 families of the flowering plancs were recorded~ Asreraceae, Fabaceae, Chenopodiaceae, Poaceae, Brassicaceae, Caryophyllaceae, Liliaceae and Zygophyllaceae were the largest families, and constitute more than 64 % of the total recorded species. Therophytes and chamaephytes were the most frequent, denoting a
typical desert lifeform spectrum. Phytochorological analyi'is revealed that 45.2 % of the studied species were uniregional, of which 23 % being native to the saharo-arabian chorotype. It also showed the decrease in the numbers of the Mediterranean species and increase of the saharo-arabian species along N-S direction fOrm the see-shore inwards till the Diffa Plateau. Classification of the vegetation was analysed using TWINSPAN technique resulted in the recognition of five vegetation groups, each of definite floristic composition and environmental characteristics, and could be linked to a specific habitat. Haloxylon salicornicum occupied the fOot of the Diffa Plateau, Haloxylon salicornicum- Thymelaea hirsura characterised the sand plains, Thymelaea hirsura-Anabasis articulara inhabited the non-saline depressions, Haloxylon salicornicum-Auiplex por­ rulacoides characterised the saline depressions and Salsola reuan­ dra-Limoniasrrum monoperalum on the coastal salt marshes. Ordination techniques as DCA and CCA were used to examine the relationship between the vegetation and the studied environmental parameters: electric conductivity (EC), pH, calcium carbonate, mois­ ture content, organic matter, silt, clay, K., Mg;+ and altitude. CCA axis 1 showed significant correlation with clay, moisture content, pH, Ee, K', and altitude, while CCA axis 2 was clearly related to pH, Mg;' and altitude. Species richness was correlated with Mg;., while Shannon index was correlated with Na+ and Mg;+.